Hoppers are often used to hold bulk quantities of materials such as grain, flour, sugar, or plastic beads. Hoppers can be built and used in stationary environments, such as flour elevators, or in mobile environments, such as railroad cars, cargo ships, or semi-trailer trucks. A pressurized fluid, (as used herein, a fluid can be, e.g., a gas such as compressed air, or a liquid such as water), can be used to convey such materials from a hopper to another place for storage or use. For example, a pressurized gas applied at the lower exit port of a tapered hopper can force the material coming out of the hopper into and through a pipe. It is often advantageous to apply some gas pressure to the top of the material; i.e., to seal the top and pressurize the hopper or similar container in order to urge the material out the tapered bottom of the hopper. In this art, a hopper, or similar container for holding materials such as dry particulates (e.g., flour, grain, granulated sugar, plastic pellets, etc.), that can be pressurized is sometimes called a pressure pot or a blow tank.
U.S. patent Application US 2003/0206776 A1, titled “RAILROAD HOPPER CAR UNLOADER” by William Pearson, published Nov. 6, 2003, describes a system that unloads material, such as bulk quantities of dry product, from a container, such as a railroad hopper car. The container defines an enclosed interior that holds a product and includes a product-discharge section adapted to allow the product to exit therethrough. In some conventional systems, the unloading of the railroad-hopper car occurs solely under the influence of gravity. To accomplish this, a valve provided on the bottom of the tapered discharge section of the container is opened, allowing the product to flow downwardly therethrough into a receiving apparatus. Such gravity unloading is simple and inexpensive from an equipment standpoint, but has been found to be rather inefficient. This is because the product unloads from the container at a relatively slow rate, which undesirably increases the amount of time and resources required to empty the product from the container. Also, portions of the product often coalesce and adhere to the interior of the container. When this occurs, portions of the product do not unload under the sole influence of gravity, thus requiring additional time and effort to dislodge such portions for unloading. To address these problems, some conventional railroad-hopper cars are provided with equipment that introduces pressurized fluid (called the pressurization or upper-end flow, which may be air, in some embodiments) within the container during the unloading process, which helps push the product out of the container at a rate that is faster than if the product was unloaded solely under the influence of gravity. Additionally, the flow of pressurized air within the container tends to stir up or fluidize the product therein so as to minimize the occurrence of coalescence and adherence of the product to the interior of the container. Some conventional material-unloading systems also include a product-outlet line adapted to receive material from the product-discharge section of a hopper, and to also receive pressurized fluid (called the conveying or lower-end flow, which also may be air, in some embodiments) that is used to move product from the product discharge section though the product-outlet line.
When pressure and air flow are applied to the top of the material (the upper-end flow) as well as to the exit pipe (the lower-end flow) of a pressure pot, there is an adjustment that should be made to achieve the proper amount of pressure and flow applied to the upper- and lower-end of the material to achieve the fastest material flow. If too much pressure is applied to the upper end, too much material is pushed out of the pressure pot in a given amount of time, which clogs the exit pipe and stops the material flow. If too much pressure is applied to the lower end, then more carrier fluid (e.g., air) and less material flows out the exit pipe.
Thus, there is a need for improved methods and mechanisms to automatically adjust the balance of flow and pressure between the upper end and lower end of a pressure pot.